Control means for high speed hoist

ABSTRACT

A control means for a high speed electric hoist or crane having an induction motor permits motor operation in the &#39;&#39;&#39;&#39;raise&#39;&#39;&#39;&#39; or &#39;&#39;&#39;&#39;lower&#39;&#39;&#39;&#39; direction at controlled speeds up to full load hoisting speed (i.e., the approximately synchronous speed of the motor). The control means also permits the motor to operate automatically in the &#39;&#39;&#39;&#39;lower&#39;&#39;&#39;&#39; direction so as to differentiate between a &#39;&#39;&#39;&#39;light&#39;&#39;&#39;&#39; and a &#39;&#39;&#39;&#39;heavy&#39;&#39;&#39;&#39; load and to allow a light load to free fall up to 275 percent of motor synchronous speed but forcing a heavy load to be lowered normally at a restrained speed of about 100 percent of motor synchronous speed.

United States Patent 1191 Stone et al.

[111 3,772,579 1451 Nov. 13, 1973 CONTROL MEANS FOR HIGH SPEED 3,248,6254/1966 Wycoff 318/203 R HOIST Inventors: David W. Stone, Franklin, Wis.;Primary Examiner-0911c Rubinwn Manfred A. Hansen, Renton, Wash.Attorney-James Nlnes [73] Assignee: llarnischfeger Corporation, W. W

Mi u ss r W 6 1 ABSTRACT [22] Filed: 1972 A control means for a highspeed electric hoist or [211 APPL 2 7 7 crane having an induction motorpermits motor operation in the raise or lower direction at controlled 1speeds up to full load hoisting speed (i.e., the approxi- [52] US Cl318/203 R, 318/204, 318/209 mate, synchronous speed f the motor) Thecomm] [5 Int. Clv means l p it th motor t p t t ti lly [58] new of send318/" 2041 in the lower direction so as to differentiate between 318/209a light and a heavy load and to allow a light load to free fall up to275 percent of motor synchronous [56] cued 1 speed but forcing a heavyload to be lowered normally UNITED STATES PATENTS I at a restrainedspeed of about percent of motor 2,963,634 12/1960 Cortelli et a1 318/203R x synchronflus p 2,766,415 10/1956 Schurr 318/203 R X 3,039,036 6/1962Wendelburg ct a1 318/203 R x 8 Chill, B 2,846,631 8/1958 Vogt 318/203 RX 2,823,341 2/1958 Smith et al 318/203 R X MECHANICAL MOTOR WOUND RoToRBRAKE MOTO M EDDY CURRENT H LOAD BRAKE I ,1 1'1 Jul; i I 1 16 f1 11 1 LI 12 BRAKE SECONDARY K17 fii RECTIFIER 13 PRIMARY 18 L3 "L RESISTANCENETWORK 111 11 'L p Y L2 131 L 1 m l4Al3Al2Al1/1 L1 1 l I 5A -4A 3A -2A--1A 130 R 11 L 1 1 1 11 W Li I Q; T1 1 2 1 .1 MJ T7 W W L. Y a J 12 5123 119 118 99 81 122 121 120 PATENTI-Illuuv 13 I915 8772.579

SHEET I; 0F 9 II HOI ING I IHOISTING) I LOADING AVAILABLE TO PICK UPLOAD E 200010" DETECTOR RELAY TO ALLOW EDDY CURRENT BRAKE TO BE TURNEDOFF SO THE MOTOR' CAN ACCELLERATE TO NEAR SYNCHRONOUS SPEED LOWE RINGTQQQUE 109 1., 50|o 0% HOI STING TORQUE REGENERATION MODULE PUTS OUTSIGNAL IE (POWERED LOWERING) MOTOR DRIVEN DOWNWARD AT SUBSYNCHRONOUSSPEED II (REGENERATIVE LOWERING BRAKING) LOAD RELAY AND TIME DELAY RELAYREMAIN ENERGIZED FOR REGENERA- TIVE LOWERING OF HEAVY LOADS (ABOVE 15IoOF RATED TORQUE) LOAD RELAY AND TIME DELAY DROPOUT TO SWITCH OUT EDDYCURRENT BRAKE FOR HIGH SPEED LOWERING OF LIGHT LOADS (BELOW 15Io OFRATED TORQUE) 3OOI0- LOAD IN FREE FALL g N'IL SPEED APPROACHES l OFMOTOR SYNCI-IRONOUS SPEED L%\ Q/ E F NG EDDY CURRENT BRAKE EXITATIONREGULATED BY FREQUENCY DETECTOR MODULE TO HOLD MOTOR SPEED TO ABOUT275Io OF 2 SYNCHRONOUS SPEED PAIENIEDMUY 13 ms 3.772.579

SHEET 5 OF 9 Q 'SQ IRON STATOR ASSEMBLY COIL FAN ROTOR 71 BEARING EARINGEDDY CURRENT LOAD BRAKE FIGS MASTER CONTROL SWITCH (OFF POSITION) FIG. 3

SHEET 80F 9 PATENTEDNOV 13 1975 FIG. 7 I

E FREQUENCY DETECTOR T MODULE 1 $1 1 l 1H l 1 REFERENF l R SECTION I 1 11 1.9 1 1 A1 2 I 41 fio a J MASTER RECTI F IE I l I I 1 l ,..111lLr 1PATENTEDImv 13 1915 3,772,579

SHEET 7 BF 9 LOAD BRAKE SPEED- TORQUE CHARACTERISTICS FIG. 6

PATENTEU NOV 13 975 SHEET 8 OF 9 PAIENTEUnnv 13 ms 3. 772,579

SHEET 9 OF 9 w O 9 w wm Vii lli i iilillilllll llllIi 1% 1 CONTROL MEANSFOR HIGH SPEED HOIST BACKGROUND OF THE INVENTION 1. Field of Use Thisinvention relates to control means for hoists or cranes which effectcontrolled raise and lower operations and also effect automatic highspeed lower operation at two different speeds under light and heavyloads.

2. Description of the Prior Art High speed AC electric hoists used, forexample to transport concrete buckets to pouring levels on high risebuildings must operate at the highest rate of speed possible consistentwith safety requirements. Heretofore, such hoists had control means toeffect controlled raise and lower operations up to a certain speed (fullload hoisting speed) and automatic high speed lower operation at somesingle speed well in excess of that speed. Such control means, whenoperating in automatic high speed lower, did not distinguish speedwisebetween light or heavy loads. Thus, the braking means brought into playto maintain constant high speed lowering tended to be potentially lesseffective when heavy loads were involved and increased the danger of arunaway load.

SUMMARY OF THE PRESENT INVENTION The present invention contemplates ahigh speed hoist comprising a hoist drum on a shaft driven by an ACelectric motor. The hoist control means'include an electrically operablemechanical brake for the hoist drum (i.e., motor shaft), a magnetic oreddy current brake coupled to the shaft, and an electric controller foroperating the motor, the mechanical brake and the magnetic brake.

The hoist control means permits motor operation in the raise or lowerdirection at controlled speeds up to full load hoisting speed (i.e., theapproximately synchronous speed of the motor). The control means alsopermits the motor to operate automatically in the lower" direction so asto allow an empty bucket to free fall up to 275 percent of full loadhoisting speed.

However, any heavier load that cannot be safely handled at this highspeed will be restrained to about 100 percent of full hoisting speed.

The electric controller of the control means comprises certaincomponents or modules which come into play during raise" and loweroperation of the motor and during lightly-loaded or heavily loaded lowerconditions, namely, a load detector module including a load detectorrelay, a regeneration module, a magnetic brake guard control moduleincluding a time delayed relay, a frequency detection module, a magneticamplifier module, a controlled rectifier module, and an antihunt module.The time delayed relay and guard control module together, in effect,constitute a time delay relay.

The hoist control means operates as follows. Before electric power isapplied, the motor shaft is held stationary by the mechanical brake.After electric power is applied, the magnetic brake is energized to anoff position" level to exert a nominal retarding torque to meansincreases from the off position level to a maximum level. The stallmotor torque is normally 10 percent for lowering and 140 percent forhoisting. When the motor is operated at full-speed raise or lower,permissive interlocking functions are carried out by the controller asfollows. The load detector module senses when the motor delivers 15percent or more of full load torque and the load detector relay picks up(this relay also drops out at slightly lesser torque, i.e., 12 to 13percent). The regeneration module senses when the motor exceedssynchronous speed and provides a control signal. The magnetic brakeguard control module causes its time delayed relay (normally picked up)to drop outafter a short time delay in response to receiving both thecontrol signal from the regeneration module and drop out of the loaddetector relay.

The net functional result of the operation of these modules is asfollows. In the slow raise or slow lower conditions, the motoraccelerates, stabilizes at a slow speed and continues running untilstopped by the operator or by limit switches. In the full speed lowercondition, stabilization of motor speed will occur at a running pointwhich will be in one of three general conditions, namely:sub-synchronous (driving a light load down); restrained fall at percentof hoisting speed with a heavy load causing the motor to regenerate morethan 15 percent of full load torque; or

free fall to 275 percent of full load hoisting speed and then controlledwith a light load causing the motor to regenerate less than 15 percentof full'load torque. If full speed raise is selected, the motor will beaccellerated only if the time delay relay and load detector relay arepicked up. The motor will continue until there is operator or limitswitch intervention.

All three of these lowering conditions are stable and will continueuntil the motor is slowed or stopped by the operator or by limitswitches which effect progressive slow down and stopping of the motorand simulate the effect of the operators return of a master controlswitch toward neutral position.

In condition (1), the load detector relay may drop out, but nothingelse.

In condition (2), the load detector relay drops out. The regenerationmodule provides a control signal at synchronous speed, but before thetime delayed relay drops out, the load detector relay picks up again.Therefore, the time delayed relay remains picked up.

In condition (3), the load detector relay drops out. The regenerationmodule turns on at synchronous speed and, since the load detector relaydoes not pick up again, the time delayed relay eventually drops out.This causes all motor accelerator contacts to open and, with thesecondary winding of the motor open, the motor exerts no torque and thesecondary voltage and frequency is applied to the frequency detectormodule. The light load is then in free fall, restrained only byfriction, windage and mass. When it accelerates to approximately 270percent of full load hoist speed, the frequency detector module providesan output signal which starts to increase the magnetic brake excitationand the motor speed stabilizes at about 275 percent of full loadhoisting speed.

DRAWINGS FIG. 1 (sheets 1, 2 and 3) is a schematic diagram of a hoistand control means therefor in accordance with the invention;

FIG. 2 is a graph wherein motor speed is plotted against motor torqueunder various operating conditions, as described in legends on thegraph;

FIG. 3 is a side view of the master control switch shown schematicallyin FIG. 1; I

FIG. 4 is a diagrammatic view of the frequency detector module shown inFIG. I and includes details of a master reference rectifier;

FIG. 5 is a cross-section view of the magnetic or eddy current loadbrake shown in FIG. 1;

FIG. 6 is a graph showing the speed-torque characteristics of themagnetic load brake shown in FIGS. 1 and 3;

FIG. 7 is a diagrammatic view of the magnetic amplifier module shown inFIG. 1;

FIG. 8 is a diagrammatic view of the load detector module shown in FIG.1;

FIG. 9 is a diagrammatic view of the regeneration module shown in FIG.1; and

FIG. 10 is a diagrammatic view of the guard control module shown in FIG.1;

DESCRIPTION OF A PREFERRED EMBODIMENT General Arrangement and OperationFIG. 1 (sheet 1) shows a hoist comprising a hoist drum 10 on a shaft 11with a cable 12 to which a load 13 is attached. Shaft 11 is driven by awound rotor induction motor 14 having primary and secondary windings. Avariable resistance network 15 including accelerator contacts isconnected to the motor secondary windings. A spring applied electricallyreleasable mechanical holding brake 16 is provided for shaft 11. An eddycurrent or magnetic load brake 17 is also provided for motor shaft 11.The primary of motor 14 is connectible for hoist and lower operation toan electrical power source comprising ac power lines L1, L2 and L3 byreversing contractor 18.

FIG. 1 (sheets 2 and 3) also shows a controlller for operating contactorI8 and motor 14, mechanical brake l6, eddy current brake l7, andresistance network 15. As FIG. 1 (sheet 2) shows, the controllercomprises a control switch 19 having first and second point positions inboth lower and raise (a total of five contact circuits) and push-buttonswitches, relays and limit switches hereinafter described. As FIG. 1(sheet 3) shows, the controller further comprises a regeneration module20, a load detector module 21, and its load dector relay 22, a guardcontrol module 23 and its time delayed relay 24, a frequency detectormodule 25, a magnetic amplifier module 26, a controlled rectifier module27 and an anti-hunt module 28. All modules are hereinafter described indetail.

Before power is applied, shaft 11 is held stationary by mechanical brake16. After power is applied, eddy current brake 17 is energized to an offposition level to exert a nominal retarding torque on shaft 11 toprevent runaway if mechanical brake l6 fails. When master control switch19 is moved to a first position to operate motor 14 for operation ineither the raise or lower direction, mechanical brake 16 releases andeddy current brake 17 energization is increased from off position" levelto a "maximum level. Stall motor torque exerted on shaft 11 is 10percent for lowering ad 140 percent for hoisting. When master controlswitch 19 is moved beyond first point to second point position tooperate motor 14 at full raise or lower speed, permissive interlockingfunctions are carried out by the controller as follows, with stall motortorque first going to 140 percent as during hoisting.

Load detector module 221 senses when motor 14 delivers 15 percent ormore of full load torque and causes detector relay 22 to pick up (close)its contacts 22A and 22B. Module 21 also causes relay 22 to drop out(open) its contacts at a slightly lesser torque of about 12 or 13percent. Regeneration module 20 senses when motor 14 reaches or exceedssynchronous speed and provides a control signal to guard control module23. The guard control module 23 causes its time delayed relay 24 to dropout (open) its contacts 24A and 243 after an appropriate time intervalif regeneration control module 20 is providing a signal and loaddetector module relay 22 is energized.

The result of the relays 22 and 24 both being energized when motor 14 isbeing operated in the'raise direction is to bias the guard module 23 offat the same time as 3A, 4A and 5A in the controller sequentially operatetheir contacts in resistance network 15 to remove resistance andaccelerate motor 14. Motor 14 stabilizes at a speed detennined by theload and the permanent slip resistor and continues running untildecreased or stopped by the hoist operator or slowed and stopped by theappropriate limit switches RL] and RL2.

When the motor 14 operates in the lower direction the accelleration isaccomplished in the same way as in second point raise. Since the finalpermanent resistance is the same, the reflected load will cause themotor to stabilize. The speed will be either barely subsynchronous (foreffectively no load); just over motor synchronous speed with a loadsufficiently heavy to cause the motor to regenerate more than 15 percentof full load torque; or just over motor synchronous speed with a loadcausing the motor to regenerate less than 15 percent of full loadtorque. If it is the latter case, the controller will allow the load toaccelerate the motor shaft to 275 percent of motor synchronous speed, atwhich point the eddy current brake will then regulate motor speed. Motorspeed is stable at each of the three conditions and continues untilslowed or stopped by the hoist operator or by limit switches LLl andLL2.

It is to be understood that guard module 23 is always biased on and timedelayed relay 24 is picked up (energized) at all times except when theinterlock contacts L or R of lower relay L or raise relay R are closedand contact 22A of relay 22 is open and regeneration module 20 has anoutput at its terminals 5 and 6 and sufficient time has passed. The timedelay is brought about by integration of the difference between theinternal bias in guard module 23 and the current at terminals 1 and 2 ofguard module 23 from regeneration module 20.

As movement of master control switch 19 continues, contactor 2A isenergized and this causes rapid subsequent successive energization ofthe other contactors 3A, 4A and 5A. Contactor 2A is energized at firstpoint raise and immediately in full (second point) lower. When contactor2A is energized, relay 22 picks up and closes its contacts 22A and 228.Therefore, at full raise or lower, relay 22 and time delay relay 24 arepicked up. THis, in turn picks up relay CP, which in turn removes theexcitation of eddy current brake 17.

This system uses a wound-rotor induction motor whose second point raiseand lower speeds depend only upon the motor constant, the line voltageand fixed permanent secondary resistors and the reflected shaft load.

In order to drop out or unexcite the eddy current brake 17 when goingfrom first point raise or lower to second point, both the timedelayedrelay 24 and the current (or load) sensing relay 22 must beenergized and one of their N.O. contacts on each relay closed. This isfor safety and required to prove the circuits are working.

In order to go to high speed, lower both time delayed relay 24 and thecurrent sensing relay 22 must be deenergized and another of their N.O.contacts on each relay must be open.

The first point speeds depend upon the motor constants, secondaryresistors, line voltage, eddy current brake l7 excitation and reflectedshaft load. Full load first point raise is approximately 3 percentsynchronous speed and empty bucket, first point lower is approximately 1percent synchronous speed.

Assuming that the above described sequences are carried out to effect alowering operation of the hoist,

one of the'three conditions specified hereinbefore occurs, namely:

1. The load, if any, is driven down undercontrol at some desiredsubsynchronous speed, or

2. The load descends at a restrained speed (slowly,

over 102 percent of synchronous speed) with a heavy load causing motor10 to regenerate more than percent of full load torque, or

3. Free fall at 275 percent of synchronous speed with a light load 16caused by motor 10 regenerating less than 15 percent of full loadtorque.

As previously noted, all three of these lowering conditions are stableand will continue until slowed or stopped by the operator or by thelimit switches LLl, LL2, RLl or RL2 in the control circuit. The limitswitches are arranged to effect progressive slow down and stopping ofthe motor and simulate the effect of the operators return of the mastercontrol switch toward neutral position. i

In condition (1 the load detector relay 22 may drop out, but nothingelse.

In condition (2), the load detector relay 22 drops out and theregeneration module 26 provides a control signal at synchronous speed.But before the time delayed relay 24 drops out, the load detector relay222 picks up again. Therefore, time delayed relay 24 remains picked up.

In condition (3), load detector relay 22 drops and regeneration module20 turns on at synchronous speed.-

Since load detect or relay 22 does not pick up again, time delayed relay24 eventually drops out. This drops relay 1A, which drops 2A, causes allcontacts of resistance network 15 to open and, with the secondarywinding of motor 14 open, the motor exerts no torque and the secondaryvoltage and frequency is applied to frequency detector module 25. Thelight load 13 is then in free fall, restrained only by friction, windageand mass. When it accelerates to approximately 270 percent of full loadhoist speed,-frequency detector module 25 provides an output signalwhich starts to increase the excitation of eddy current brake l7 andmotor speed stabilizes at about 275 percent of full load hoisting speed.

All of the operating conditions hereinbefore described are depicted inthe graph in FIG. 2 wherein motor speed is polotted against motor torquefor motor operation in the raise and lower directions.

A more detailed description of the construction and operation ofcontroller components is as follows.

Master Control Switch Master control switch 19, shown schematically inFIG. 1 (sheet 2) and in FIG. 3 operates contacts N, 40, 41, 42 and 43 tooperate reversing contactor 18 and resistance network 15 to establishmotor direction of speed. Section 47 of frequency detector module 25(FIG. 4) comprises a full wave rectifier 48 to convert the ac signal todc and a signal adjustment rhostat or potentiometer 49. As FIG. 1 (sheet3) shows, the output terminals 3 and 4 of section 47 of module 25 areconnected by conductors 51 and 52 to provide a variable dc speedreference signal to terminals 9 and 10 of magnetic amplifier module 26.

Master control switch 19 will not function until start button isdepressed with the induction master control switch in neutral withcontact N closed. When start button 60 is depressed, UV relay coil 61 isenergized and UV relay coil 61 is de-energized by emergency stoppushbutton 62, stop pushbutton 63, manual reset overspeed switch 64, ormotor overload contacts 65 and 66.

The desired side of reversing contactor 18 will come in to energizemotor 14 when master control switch 19 is moved to first point raise orlower position, provided the corresponding travel limit switches LLl andRLl are not open. With motor 14 energized for rotation in the desireddirection, mechanical brake l6 releases and excitation of eddy currentbrake 17 increases from the off position level to the maximumlevel.Stall motor torque is 10 percent for lower and 140 percent for raise.

Eddy Current Irake As FIG. 5 shows, eddy current brake 17 comprises aniron rotor mounted on bearings 71 on shaft 11 inside a stationary fieldassembly having an iron stator 72 and coils 73. When direct currentflows through coils 73, alternate magnetic poles are produced in stator72 (Le, north next to south, etc.) which induce alternate field in rotor70 when the latter moves. This interaction induced by eddy currents inrotor 70 produces retarding torque at various speeds, as shown in thespeed-torque graph in FIG. 6.

Excitation of the elctric brake coils 73 in eddy current brake 17 isprovided by controlled rectifier module 27 which, in turn, is operatedby magnetic amplifier module 26. Magnetic amplifier module 26, in turnis responsive to its own internal (off) bias and to the off biases fromtransformer T9 (rectified in rectifier section 47 of frequency detectormodule 25; the speed feedback signal from the secondary windings ofmotor 14 (as sensed and provided by frequency detector module 25); andan anti-signal from anti-hunt module 28.

Controlled Rectifier Module As FIG. 1 (sheets 1 and 3) shows, controlledrectifier module 27 has power input terminals and 81 which are suppliedwith power from correspondingly numbered terminals of an anodetransformer 82 connected to lines L1 and L2 of the main power supply.Module 27 comprises two SCRs 83 and 84 (silicon controller rectifiers)which, when gated, supply ac current to the electric brake coils 73 ofeddy current brake 17. The SCRs 83 and 84 block current in the forwarddirection until a positive gate signal is applied by magnetic amplifiermodule 26 to cause them to fire. The SCRs continue to conduct even ifthe gate signal is removed until anode current from transformer 82 fallsto zero and reverses. Module 27 includes a surge suppression resistor 85and capacitor 86 across the secondary of anode transformer 82 todissipate harsh transients.

Magnetic Amplifier Module As FIG. 7 shows, magnetic amplifier module 26comprises a power supply transformer 90, a self-saturating magneticamplifier havingiron cores 91 on which ac windings 92 are provided,three control windings 93, 94 and 95, and a bias winding 95a and smallrectifiers 96 in series with each ac winding 92. As FIG. 1 (sheets 1 and3) shows, the input terminals 1 and 2 of power supply transformer 90 ofmagnetic amplifier module 26 are connected by conductors 97 and 98 tocorrespondingly numbered terminals of anode transformer 82. The outputterminals 4, and 6 of magnetic amplifier module 27 are connected,respectively, to the gate of SCR 83, to one side of eddy current brakecoils 73 and the SCRs 83 and 84, and to the gate of SCR 84. The otherside of coil 73 is connected to terminal 99 of anode transformer 82 by asimilarly numbered conductor. The terminals 7 and 8 of control winding93 speed feedback signal) are connected by conductors 100 and 101 toterminals A1 and A2 of frequency detector module 225. The terminals 9and of control winding 94 (speed reference signal) are connected byconductors 52 and 51 to terminals 4 and 3 of frequency detector module25. The terminals 11 and 12 of control winding 95 (anti-hunt signal) areconnected by conductors 103 and 104 to terminals 6 and 5 of anti-huntmodule 28. The anti-hunt module 28 provides transient signals whichcompensate for system response delays which could result in hunting andcomprises a resistor 105, an adjustable potentiometer 106, and acapacitor 107.

The magnetic amplifier in module 26 is selfsaturating and, if notexcited by the control windings 93, 94 and 95 or bias winding 95a, tendsto turn the SCRs 83 and 84 full on to fully energize eddy current brakecoil 73. Control current in one or more of the control windings 93, 94and 95 or bias current in bias winding 95a resets the amplifier and itcan be made to saturate over the entire ac half cycle, partial cycle ornot at all. When the magnetic amplifier functions as an error detector,it continuously compares the off and bias signals with the speedfeedback signal (and the anti-hunt signal) and providing SCR controloutput signals at terminals 4, 5 and 6 of module 26 which are theresultant thereof.

When the odd numbered terminal of a control winding is positive with.respect to its even numbered terminal, the current in the controlwinding tends to turn the output pulse on. The reverse is true when theodd numbered terminal is negative with respect to its even numberedterminal. All of the control signals are of constant polarity except theanti-hunt signal. The values may vary from zero to a minimum, but neverreverse in polarity. The anti-hunt signal is not constant, but allowscurrent to flow in its control winding only under transient conditions.

Frequency Detector Module When master control switch 19 is in firstpoint LOWER position, motor 14 is energized but the rotor is restrainedbecause magnetic amplifier module 26 is at maximum on and load brake 17is excited. If motor 14 starts to turn, all signals remain constant. Thefrequency detector module 25 input is shorted by contacts 1A.

The frequency detector module 25 shown in FIGS. 1 and 4 has its inputterminals 7 and 12 connected across the secondary winding of motor 14 byconductors and 11 1, respectively, and provides, at its output terminalsA1 and A2, a dc speed feedback signal which is proportional to the rotorfrequency of motor 14, which in turn is proportional to motor slip andbelow motor synchronous speed. It may-be assumed that motor 14 at restproduces a frequency of 60 Hertz and at synchronous speed produces azero frequency. There is no input from the motor secondary intofrequency detector module 25 whenever contactor 1A is energized. Ifmotor 14 is driven faster than synchronous speed by an overhauling load,rotor frequency again increases. The magnitude of voltage induced in therotor (secondary) windings varies directly with frequency. As FIG. 4shows, frequency detector module 25 comprises an input transformer 112and a saturating transformer 113 saturated by rotor voltage and having asquare hysterisis loop core which tends to produce constant energypulses for each half cycle f0 input frequency. These pulses, whenrectified and filtered by the rectifiers 114 and capacitors 115, producea dc voltage signal (speed feedback signal) directly proportional tomotor frequency at terminals Al and A2.

Load Detector Module Referring to FIGS. 1 (sheet 3) and 8, the loaddetector module 21 has power supply terminals 11 and 12 which areconnected by conductors 118 and 119 to anode transformer 82. Module 12also has signal input terminals 1, 2 and 3 which are connected byconductors 120, 121 and 122, respectively, to transformers 123, 124 and125, respectively, which are connected to a portion of the permanentresistors for motor 14 to sense current conditions therein. Loaddetector module 21 which includes a signal detection section 126 and anamplifier section 127 senses when motor 14 is delivering over a maximumof 15 percent of full load torque and provides an output signal at itssignal output terminals 6 and 7 to energize relay coil 22 connectedthereto. Relay coil 22 operates relay contacts 22A and 22B. Loaddetector module 21 is designed to effect deenergization of relay coil 22if motor torque drops to between about 12 and 13 percent of full loadtorque. The load detector module 21 has an On bias in it that varieswith line voltage so that in the first approximation, the circuit tripson power and not current, i.e., shaft torque.

Regeneration Control Module Referring to FIGS. 1 (sheet 3) and 9, thefunction of regeneration control module 20 is to provide an outputsignal at its terminals 5 and 6 for guard module 23 when motor 14reaches and exceeds synchronous speed. Module 20 receives a voltageinput signal at its terminals 1 and 2 from a voltage transformer 130coupled to the main supply lines L1 and L2. Module 20 also receives acurrent input signal at its terminals 3 and 4 from a current transformer131 coupled to main supply line L2. Power for module 20 is provided atits power supply terminals 7 and 8 from a transformer 132 understood tobe connected to lines L1 and L2. The regeneration module 20 comprises arectifier section 133 to combine and rectify the voltage and currentsignals and a level detector-switching section 134 to detect when thecombined and rectified signal falls below a level and switches on apower level for delivery to signal output terminals 5 and 6.

Guard Control Module Referring to FIGS. 1 (sheet 3) and 10, the guardcontrol module 23 is designed to maintain relay 24 energized at alltimes, except under specified conditions. Module 23 comprises an inputamplifier 140 having input terminals 1 and 2 for a first control winding141. Terminal 2 is connected to terminal 5 of the regeneration module 20and to terminal 3 of a second control winding 142, and the lattersterminal 4 is connected through a resistor 143 to the terminal 7 of athird control winding 144. The latters terminal 8 is connected by aconductor 145 to terminal 10 of regeneration module 20. When the signalis present in the control winding 14] of guard control module 23 fromterminals 1 and 2, the input amplifier 140 tends to turn off a secondstage amplifier 146 of guard module 23 after a time delay. However, thepresence of an input signal at input terminals 2 and 8 to controlwindings 142 and 144 of guard module 23 (from terminals 5 and 10 of theregeneration module 20) tends to turn on module 23. Duringsubsynchronous operation only, the ON signal exists and the outputterminals A3 and A4 are energized to energize, pick up or close timedelay relay 24.

With a signal at terminals 1 and 2, the OFF signal cancels the ON signaland after a predetermined time delay output terminals A3 and A4 aredeenergized, dropping out relay 24. Power to the module is suppliedthrough terminals Al and A2 from terminals 118 and 119 of anodetransformer 82.

We claim: t

l. A hoist comprising an induction type electric motor and control meansfor operating said motor in raise and lower directions, said controlmeans comprising, a controller, electrically operable brake means forsaid motor, brake control means for controlling said brake means, firstmeans responsive to regenerative conditions in said motor to effectoperation of said brake control means, and second means responsive totorque conditions in said motor to effect operation of said brakecontrol means, said first and second means,

when said controller is operating said motor in the lower direction,being responsive to the regenerative andtorque characteristicsexhibitedby said motor when subjected to various loads in the lowerdirection to operate said brake control means to effect motor operationat a first speed which is approximately the synchronous speed of themotor when a load is sufficiently light to be non-regenerative; toeffect motor operation at a second speed which is approximately thesynchronous speed of the motor when a load is sufficiently heavy to beregenerative and is producing more than a predetermined amount oftorque; and to effect motor.

operation at a third speed which is in excess of the synchronous speedof the motor when a load is sufficiently heavy to be regenerative and isproducing less than a predetermined amount of torque.

2. A hoist according to claim 1 wherein said first speed is slightlybelow a synchronous speed, wherein said second speed is slightly abovemotor synchronous speed, and wherein said third speed is substantiallygreater than motor synchronous speed.

3. A hoist comprising a wound rotor induction type electric motor andcontrol means for operating said motor in raise and lower directions,said control means comprising:

a controller for selectively operating said motor in a least one speedrange in the raise direction and in at least a slower and faster speedrange in the lower direction; an eddy current type load brake for saidmotor; magnetic amplifier means for operating said load brake; firstmeans including a regeneration circuit and a frequency detector circuitfor sensing whether or not said motor is regenerating at least whenoperating in the lower direction and for providing a related controlsignal for effecting operation of said magnetic amplifier means; andsecond means including a load detector circuit for sensing the torque ofsaid motor at least when operating in the lower direction and forproviding a related control signal for effecting operation of saidmagnetic amplifier means, said magnetic amplifier means being operativein response to said first and second means at least when said controlleris operating said motor in the lower direction to operate said loadbrake to enable said motor: to drive a load sufficiently light to benon-regenerative at a rate of 7 speed corresponsing to approximately thesynchronous speed of said motor when said first means sense suchnon-regenerative condition; to lower a load sufficiently heavy to beregenerative and producing more than a predetermined amount of torque ata rate of speed corresponding to approximately the synchronous speed ofsaid motor when said first and second means sense such regenerative andtorque conditions; and to lower a load sufficiently heavy to beregenerative and producing less than said predetermined amount of torqueat a rate of speed corresponding to a speed greater than the synchronousspeed of said motor when said first and second means sense suchregenerative and torque conditions.

4. A hoist according to claim 3 wherein said first means sense anon-regenerative load and operates said magnetic amplifier means toeffect motor operation at a rate of speed slightly below synchronousspeed; wherein said first and second means sense a regenerative loadproducing more than said predetermined amount of torque and operate saidmagnetic amplifier means to effect motor operation at a rate of speedslightly above synchronous speed; and wherein said first and secondmeans sense a regenerative load producing less than said predeterminedamount of torque and operate said magnetic amplifier means to effectmotor operation at a rate of speed in excess of twice synchronous speed.

5. A hoist according to claim 4 wherein said predetermined amount oftorque is approximately 15 percent of full load torque.

6. A hoist according to claim 5 wherein said rate of speed in excess oftwice synchronous speed is approximately 270 percent of synchronousspeed.

7. A hoist comprising a wound rotor induction type electric motor and aneddy current type load brake for said motor and control means for saidbrake and said motor comprising:

a. a controller for selectively operating said motor in at least onespeed range in the raise direction and in at least a slower speed rangeand a faster speed range in the lower direction,

said controller comprising a first relay;

b. a magnetic amplifier for controlling energization of said brake tocontrol motor speed;

c. a regeneration circuit responsive to motor speed in said faster speedrange to provide an output signal when motor speed exceeds synchronousspeed;

d. a frequency detector circuit responsive to motor speed in said fasterspeed range to provide an output signal when motor speed exceedssynchronous speed, provided said controller effects connection of saidfrequency detector circuit to said motor,

e. a load detector circuit responsive to motor torque when said motor isoperating in the lower direction to operate a second relay when motortorque exceeds a predetermined value and to. de-energize said secondrelay when motor torque is slightly below said value; a

f. a guard circuit having a third relay, said guard circuit effectingoperation of said third relay after a predetermined interval of time'inresponse to an output signal from said regeneration circuit, providedsaid second relay is in a predetermined condition;

g, and a magnetic amplifier firing circuit for controlling said brakeand responsive:

i. to operation of said controller in at least said slower speed rangeto effect maximum energization of said brake;

ii. to operation of said controller in said faster speed range, whensaid second relay and said third relay have been at least momentarilyoperated simultaneously and said first relay is'operated as a resultthereof, to effect total deenergization of said brake to permit saidmotor to operate at approximately synchronous speed, and

iii. to operation of said controller in said faster speed range whensaid second relay is operated to effect operation of said third relay,thereby effecting an output signal from said frequency detector circuit,and said first relay is operated and is responsive to said output signalfrom said frequency detector circuit to effect increased energization ofsaid brake to limit motor speed to a speed substantially in excess ofsynchronous speed.

8. A hoist comprising a wound rotor induction type electric motor and aneddy current type load brake for said motor and control means for saidbrake and said motor comprising:

d. a frequency detector circuit responsive to motor speed in said fasterspeed range to provide an out-.

put signal when motor speed exceeds synchronous speed, provided saidcontroller effects connection of said frequency detector circuit to saidmotor, e. a load detector circuit responsive to motor torque when saidmotor is operating in the lower direction to energize asecond relay andclose its contacts when motor torque exceeds a predetermined value andto de-energize said second relay and open its contacts when motor torqueis slightly below said value; 4

f. a guard circuit having a normally energized thir relay with contactswhich are closed when said third relay is energized, said guard circuiteffecting de-energization of said third relay after a predeterminedinterval of time in response to an output signal from said regenerationcircuit, provided said second relay is de-energized;

g. and a magnetic amplifier firing circuit for controlling said brakeand responsive:

i. to operation of said controller in at least said slower speed rangeto effect maximum energization of said brake;

ii. to operation of said controller in said faster speed range, whensaid second relay and said third relay have been at least momentarilyenergized simultaneously and said first relay is energized and remainsenergized as a result thereof,

to effect total de-energization of said brake to permit said motor tooperate at approximately synchronous speed; and

iii. to operation of said controller in said faster speed range whensaid second relay is deenergized to effect de-energization of said thirdrelay, said de-energization of said third relay occurring when saidsecond relay is de-energized thereby removing torque from said motor andeffecting an output signal from said frequency detector circuit, andsaid first relay is energized and is responsive to said output signalfrom said frequency detector 'circuit to effect increased energizationof said brake to limit motor speed to a speed substantially in excess ofsynchronous speed.

1. A hoist comprising an induction type electric motor and control meansfor operating said motor in raise and lower directions, said controlmeans comprising, a controller, electrically operable brake means forsaid motor, brake control means for controlling said brake means, firstmeans responsive to regenerative conditions in said motor to effectoperation of said brake control means, and second means responsive totorque conditions in said motor to effect operation of said brakecontrol means, said first and second means, when said controller isoperating said motor in the lower direction, being responsive to theregenerative and torque characteristics exhibited by said motor whensubjected to various loads in the lower direction to operate said brakecontrol means to effect motor operation at a first speed which isapproximately the synchronous speed of the motor when a load issufficiently light to be non-regenerative; to effect motor operation ata second speed which is approximately the synchronous speed of the motorwhen a load is sufficiently heavy to be regenerative and is producingmore than a predetermined amount of torque; and to effect motoroperation at a third speed which is in excess of the synchronous speedof the motor when a load is sufficiently heavy to be regenerative and isproducing less than a predetermined amount of torque.
 2. A hoistaccording to claim 1 wherein said first speed is slightly below asynchronous speed, wherein said second speed is slightly above motorsynchronous speed, and wherein said third sPeed is substantially greaterthan motor synchronous speed.
 3. A hoist comprising a wound rotorinduction type electric motor and control means for operating said motorin raise and lower directions, said control means comprising: acontroller for selectively operating said motor in at least one speedrange in the raise direction and in at least a slower and faster speedrange in the lower direction; an eddy current type load brake for saidmotor; magnetic amplifier means for operating said load brake; firstmeans including a regeneration circuit and a frequency detector circuitfor sensing whether or not said motor is regenerating at least whenoperating in the lower direction and for providing a related controlsignal for effecting operation of said magnetic amplifier means; andsecond means including a load detector circuit for sensing the torque ofsaid motor at least when operating in the lower direction and forproviding a related control signal for effecting operation of saidmagnetic amplifier means, said magnetic amplifier means being operativein response to said first and second means at least when said controlleris operating said motor in the lower direction to operate said loadbrake to enable said motor: to drive a load sufficiently light to benon-regenerative at a rate of speed corresponsing to approximately thesynchronous speed of said motor when said first means sense suchnon-regenerative condition; to lower a load sufficiently heavy to beregenerative and producing more than a predetermined amount of torque ata rate of speed corresponding to approximately the synchronous speed ofsaid motor when said first and second means sense such regenerative andtorque conditions; and to lower a load sufficiently heavy to beregenerative and producing less than said predetermined amount of torqueat a rate of speed corresponding to a speed greater than the synchronousspeed of said motor when said first and second means sense suchregenerative and torque conditions.
 4. A hoist according to claim 3wherein said first means sense a non-regenerative load and operates saidmagnetic amplifier means to effect motor operation at a rate of speedslightly below synchronous speed; wherein said first and second meanssense a regenerative load producing more than said predetermined amountof torque and operate said magnetic amplifier means to effect motoroperation at a rate of speed slightly above synchronous speed; andwherein said first and second means sense a regenerative load producingless than said predetermined amount of torque and operate said magneticamplifier means to effect motor operation at a rate of speed in excessof twice synchronous speed.
 5. A hoist according to claim 4 wherein saidpredetermined amount of torque is approximately 15 percent of full loadtorque.
 6. A hoist according to claim 5 wherein said rate of speed inexcess of twice synchronous speed is approximately 270 percent ofsynchronous speed.
 7. A hoist comprising a wound rotor induction typeelectric motor and an eddy current type load brake for said motor andcontrol means for said brake and said motor comprising: a. a controllerfor selectively operating said motor in at least one speed range in theraise direction and in at least a slower speed range and a faster speedrange in the lower direction, said controller comprising a first relay;b. a magnetic amplifier for controlling energization of said brake tocontrol motor speed; c. a regeneration circuit responsive to motor speedin said faster speed range to provide an output signal when motor speedexceeds synchronous speed; d. a frequency detector circuit responsive tomotor speed in said faster speed range to provide an output signal whenmotor speed exceeds synchronous speed, provided said controller effectsconnection of said frequency detector circuit to said motor, e. a loaddetector circuit responsive to motor torque when said motor is operatingin the lower direction To operate a second relay when motor torqueexceeds a predetermined value and to de-energize said second relay whenmotor torque is slightly below said value; f. a guard circuit having athird relay, said guard circuit effecting operation of said third relayafter a predetermined interval of time in response to an output signalfrom said regeneration circuit, provided said second relay is in apredetermined condition; g. and a magnetic amplifier firing circuit forcontrolling said brake and responsive: i. to operation of saidcontroller in at least said slower speed range to effect maximumenergization of said brake; ii. to operation of said controller in saidfaster speed range, when said second relay and said third relay havebeen at least momentarily operated simultaneously and said first relayis operated as a result thereof, to effect total deenergization of saidbrake to permit said motor to operate at approximately synchronousspeed, and iii. to operation of said controller in said faster speedrange when said second relay is operated to effect operation of saidthird relay, thereby effecting an output signal from said frequencydetector circuit, and said first relay is operated and is responsive tosaid output signal from said frequency detector circuit to effectincreased energization of said brake to limit motor speed to a speedsubstantially in excess of synchronous speed.
 8. A hoist comprising awound rotor induction type electric motor and an eddy current type loadbrake for said motor and control means for said brake and said motorcomprising: a. a controller for selectively operating said motor in atleast one speed range in the raise direction and in at least a slowerspeed range and a faster speed range in the lower direction, saidcontroller comprising a first relay; b. a magnetic amplifier forcontrolling energization of said brake to control motor speed; c. aregeneration circuit responsive to motor speed in said faster speedrange to provide an output signal when motor speed exceeds synchronousspeed; d. a frequency detector circuit responsive to motor speed in saidfaster speed range to provide an output signal when motor speed exceedssynchronous speed, provided said controller effects connection of saidfrequency detector circuit to said motor, e. a load detector circuitresponsive to motor torque when said motor is operating in the lowerdirection to energize a second relay and close its contacts when motortorque exceeds a predetermined value and to de-energize said secondrelay and open its contacts when motor torque is slightly below saidvalue; f. a guard circuit having a normally energized third relay withcontacts which are closed when said third relay is energized, said guardcircuit effecting de-energization of said third relay after apredetermined interval of time in response to an output signal from saidregeneration circuit, provided said second relay is de-energized; g. anda magnetic amplifier firing circuit for controlling said brake andresponsive: i. to operation of said controller in at least said slowerspeed range to effect maximum energization of said brake; ii. tooperation of said controller in said faster speed range, when saidsecond relay and said third relay have been at least momentarilyenergized simultaneously and said first relay is energized and remainsenergized as a result thereof, to effect total de-energization of saidbrake to permit said motor to operate at approximately synchronousspeed; and iii. to operation of said controller in said faster speedrange when said second relay is de-energized to effect de-energizationof said third relay, said de-energization of said third relay occurringwhen said second relay is de-energized thereby removing torque from saidmotor and effecting an output signal from said frequency detectorcircuit, and said first relay is energized and is responsive to saidoutput signal from said frequency detEctor circuit to effect increasedenergization of said brake to limit motor speed to a speed substantiallyin excess of synchronous speed.